Forensics experts search for evidence outside the French embassy, where unidentified attackers threw an explosive device causing a small blast, in Athens, Greece, November 10, 2016. REUTERS/Alkis Konstantinidis

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ATHENS (Reuters) - Unidentified attackers on a motorcycle threw an explosive device at the French embassy in central Athens early on Thursday, wounding a guard, police said, in an attack that came less than a week before U.S. President Barack Obama visits the city.

"It was probably a hand grenade," one official told Reuters. "The building was not damaged, only externally, on the pavement. One officer, who was at the spot, was slightly injured."

The attackers were riding a motorcycle, according to footage from security cameras, another official said.

The explosion was heard in central Athens.

Small-scale attacks on businesses, police, politicians and embassies are frequent in Greece, with its long history of political violence.